This invention relates to inductors. In particular, this invention relates to planar microstrip inductors.
Microstrip inductors are typically planar conductive materials deposited onto a dielectric substrate providing a fixed amount of inductance for an electronic circuit. As is well known in the art, any length of conductive material or metal will inherently include some amount of inductance and increasing the length of a conductor and/or changing the physical configuration of a conductor can increase the inductance provided by an inductor in a reduced space.
For example, winding a piece of wire, having some nominal amount of inductance when it is a linear conductor, around another material (air, a dielectric, or metal, for example) can increase the inductance of wire substantially. Microstrip conductors frequently wind a planar conductor deposited on to a substrate in a spiral pattern to increase the inductance between the terminals of the planar conductor as well. (It is also known that changing the physical dimensions of a planar conductor on a substrate will also affect its inductance.)
Some prior art microstrip inductors employ planar conductive materials on a substrate which spiral in inwardly (or outwardly) on a dielectric substrate providing an increased amount of inductance at the terminals of the planar material. When a conductive material, such as a metal, is deposited onto a planar substrate with a spiral orientation, the prior art required that the connection node at the inner focus of the spiral be made accessible by means of a jumper wire physically bridging the windings of the spiral. This jumper wire to the inside of the spiral was known to break, change the desired value of the inductance of the spiral somewhat unpredictably, and increase the manufacturing cost requiring manual connection of the jumper lead to the spiral in many applications. A microstrip inductor that precludes the use of a jumper wire to connect a spiral microstrip inductor at both ends would be an improvement over the prior art.